Thin film metal particulates are expensive, because existing process to make them, like those described in U.S. Pat. Nos. 4,879,140 or 5,100,599, use exotic equipment such as plasma generators or vacuum chambers, or are labor intensive, small scale processes like photolithography. The prior art particulates are not readily produced in reasonable volume, and cost as much as $5,000/oz. At these prices, paints that use the particulates as the pigment are only suitable for highly specialized applications. There is a need for a lower cost, higher volume process for rapidly and reliably making thin film metal particulates usable as paint pigments.
U.S. Pat. No. 5,895,524 describes an inexpensive method to rapidly manufacture thin film metal particulates usable as paint pigments. The method involves immersing a metallized sheet of fluorinated ethylene propylene (FEP) first in an aqueous base and then in an aqueous acid to loosen and release the metal from the FEP. The particulates are brushed from the FEP into the acid tank, and are recovered. The FEP is reusable. The particulates are usually aluminum or germanium metal having a thickness of about 900 to 1100 .ANG., and preferably, 1000 .ANG..
The method may also include ultrasonically vibrating the metallized sheet following the immersions.
For making aluminum particulates, the preferred base is 7% Na.sub.2 CO.sub.3 and the preferred acid is 0.01-0.1 N acetic acid. For making germanium particulates, the preferred base is 2.5 N NaOH, since this metal is harder to loosen from the FEP. The acid bath neutralizes the basic reaction between the metal film and base.